1. The Field of the Invention
The present invention relates to a biological observation apparatus and method and, more particularly, to a biological observation apparatus and method which use a sound wave and light to obtain information indicative of internal states of living tissue.
2. Related Art
In recent years, as optical tomographic imaging for a living body, there have been known optical CT (computed tomography), optical coherence tomography (hereinafter, referred to as “OCT”), and photoacoustic tomography.
The optical CT utilizes near-infrared light of a wavelength ranging from 700 nm to 1200 nm, which is comparatively weakly influenced by scattering in a living body. Therefore, the optical CT enables to obtain tomograms of deep parts in a living body, such as up to several centimeters under a mucous membrane.
The OCT, which utilizes interference, can obtain tomographic images of a living body up to a depth of about 2 mm with high resolution (several μm to several tens of μm) in a short time. The OCT has already been put into practice in diagnosing retinopathy in the ophthalmic field. Therefore, OCT has attracted very keen interest in the medical world.
Although the optical CT can obtain information on a deep part of a living body, its spatial resolution is as low as several millimeters. In contrast, it is difficult for the OCT to perform observation at a depth of about 2 mm or more under a mucous membrane and to provide a good quality image of tumor tissue, such as a cancer. This is because the optical coherence is greatly disturbed by the influence of absorption of blood or strong scattering in the deep parts of a living body and tumor tissue.
Considering this situation, a technique for obtaining internal information of a living body other than using optical CT and OCT has been disclosed in Japanese Patent Laid-open Publication No. 2000-88743. In this technique, ultrasound waves and light are radiated into a target portion inside a living body in order to detect how much the light is modulated by the ultrasound wave in the target portion. Thereby, information on the target portion of the living body can be obtained.
Generally, when treating tumor tissue such as a cancer, a proper technique is selected depending on the condition of an observed portion including the tumor tissue and the degree of invasion in the portion. Therefore, when treating tumor tissue such as a cancer, it is necessary to recognize an area, where the boundary between the tumor tissue and normal tissue exists, located in the depth direction of the target portion, before a technique is selected.
However, according to the optical measurement apparatus disclosed in the Japanese Patent Laid-open Publication No. 2000-88743, an area where the boundary between tumor tissue and normal tissue exists cannot be defined when the condition for obtaining information on the living body is not suitable. Consequently, there is a problem that the surgeon is excessively burdened during a surgical operation on tumor tissue.